In recent years, development of displays has been remarkable. Liquid crystal displays (LCD), electroluminescence displays (EL), field emission displays (FED), or the like are used as display devices for business machines such as personal computers and word processors, and display devices for control systems in factories. These displays have a sandwich structure in which a display device is held between transparent conductive oxides.
A mainstream material for such a transparent conductive oxide is indium tin oxide (hereinafter occasionally abbreviated as “ITO”) prepared by a sputtering method, an ion plating method, or a vapor deposition method as described in Non-Patent Document 1.
ITO is composed of indium oxide and tin oxide, possesses excellent transparency and conductivity, can be etched with a strong acid, and exhibits high adhesion to a substrate. IZO has the same properties as those of ITO. In addition, IZO is excellent in etchability with a weak acid, and a highly minute electrode can be obtained from IZO.
Recently, due to the rapid popularization of flat panel displays (FPDs), there are increasing concerns about the supply shortage of indium which is the major raw material of transparent electrodes and indispensable for FPDs. As compared with zinc and tin, indium may have hazardous properties. In view of such potential hazardous properties, restriction in the amount of indium used has been desired. A target for a transparent conductive film such as ITO and IZO has a high indium content (80 to 90 atomic percent). Under such circumstances, reduction in the amount of indium in an ITO or IZO target has been strongly desired.
As for a target composed of IZO, to prevent generation of nodules and suppress abnormal electrical discharge, incorporation of a hexagonal layered compound of In2O3(ZnO)m, wherein m is an integer of 2 to 20, with a crystal grain diameter of 5 μm or less has been investigated (Patent Documents 1 and 2).
Patent Document 1: WO01/038599
Patent Document 2: JP-A-06-234565
Non-Patent Document 1: “Technology of Transparent Conductive Film” edited by The 166th Committee of Transparent Oxide and Photoelectron Material, Japan Society for Promotion of Science, Ohmsha, Ltd. (1999)
An object of the invention is to provide a high-density, low-resistance target with a reduced amount of indium, as well as a transparent conductive film and a transparent electrode for touch panels prepared using this target.